Optical networks using wavelength-division multiplexing (WDM) are being widely used with the increasing demand for telecommunication (for example, see Japanese Laid-open Patent Publication No. 2012-257002). WDM is a technique of multiplexing and transmitting a plurality of optical signals at different wavelengths. WDM, for example, enables multiplexing and transmitting of 40-channel optical signals, each at a transmission rate of 40 Gbps, as a wavelength-division multiplex optical signal (hereinafter referred to as a multiplex optical signal) at 1.6 Tbps.
WDM is used for an optical transmission apparatus such as a reconfigurable optical add-drop multiplexer (ROADM) apparatus. The ROADM apparatus includes a plurality of optical transceivers that are also called transponders, for example. The plurality of optical transceivers transmit and receive optical signals at mutually different wavelengths to and from external networks.
The ROADM apparatus multiplexes optical signals at different wavelengths input from the plurality of optical transceivers and transmits the resulting multiplex optical signal to a node in a certain path. The ROADM apparatus receives each multiplex optical signal from a node in a corresponding path, demultiplexes the multiplex optical signal into optical signals at arbitrary wavelengths, and outputs the optical signals to the plurality of optical transceivers. Wavelength selective switches (WSSs), for example, multiplex the optical signals and demultiplex the multiplex optical signals. Accordingly, the ROADM apparatus adds and drops optical signals at arbitrary wavelengths.
Such an ROADM apparatus may have a colorless, directionless, and contentionless (CDC) function. The CDC function refers to a function of transmitting added and dropped optical signals to optical transceivers without signal collision regardless of the wavelength and path.
In a case of dropping optical signals at an ROADM apparatus having a CDC function, in order to compensate for losses at an add/drop unit, a plurality of amplifiers provided in an amplifier array device amplify the respective multiplex optical signals input from the respective paths. The amplified multiplex optical signals are then input to a multicast switch (MCS) unit. In the MCS device, each optical switch selects a multiplex optical signal from a certain path for a corresponding optical transceiver, and the optical transceiver receives the multiplex optical signal. The optical transceiver may receive an optical signal at an arbitrary wavelength obtained as a result of, for example, demultiplexing of the multiplex optical signal by a WSS.
The amplifier array device and the MCS device are coupled to each other via, for example, multi-fiber push-on (MPO) connectors and an MPO cable. The MPO cable is an optical cable including a plurality of cores for transmitting a plurality of light beams, and the MPO connector is an optical connector used to connect the MPO cable.
If the MPO cable is disconnected between the amplifier array device and the MCS device, intense light that has been amplified by the amplifiers might leak outside the apparatus. Accordingly, connection of the MPO cable is checked to ensure that it is safe for the human body.
It is possible to check the connection of the MPO cable between the amplifier array device and the MCS device if, for example, there are provided light receivers that are the same as the amplifiers in number and that detect the power of the optical signals output from the respective amplifiers in the amplifier array device through the MPO cable. However, a plurality of light receivers have to be provided in this case, and accordingly, the apparatus becomes a large-scale apparatus, and the cost and mounting area are increased. Therefore, it is desirable that the connection of the optical cable is checked with a small-scale configuration.